Preparation and characterization of novel CuClSe2 semiconductor thin film

CuClSe₂ was synthesized by solid-state reaction between copper chloride and selenium at 300 °C. CuClSe₂ thin film was prepared on a glass substrate by pulsed laser deposition (PLD) method. XRD (X-ray diffraction) analysis revealed that the CuClSe₂ thin film has a preferred surface orientation parallel to (006). The transmittance and reflectance spectra of the film indicated that the compound is an indirect band gap material; the energy band gap is about 1.45 eV; its absorption coefficients are in the range of 10⁴-10⁵ cm^− 1 when the wavelength is shorter than 720 nm. The melting point of CuClSe₂ is about 328 °C. These results show that CuClSe₂ is a potential absorber layer material applied in solar cells.     

Nanostructured Cu2O thin film electrodes prepared by electrodeposition for rechargeable lithium batteries

Uniform films of Cu₂O with thickness below 1 μm were prepared from a Cu(II) lactate solution. The deposits were compact and of high purity with the particle size varying from 60 to 400 nm. They were tested as electrodes in lithium batteries and their electrochemical response was consistent with the Cu₂O + 2e⁻ + 2Li⁺ ↔ 2Cu + Li₂O reaction. Nevertheless, the reversibility of this reaction was dependent on thickness. Kinetic factors associated with the poor electronic conductivity of Cu₂O could account for the relevance of the influence of film thickness. The thinnest film, about 300 nm thick, exhibited the best electrochemical performance by sustaining a specific capacity as high as 350 Ah kg^− 1.     

Cu2O thin films deposited by reactive direct current magnetron sputtering

The Cu₂O thin films were prepared on quartz substrate by reactive direct current magnetron sputtering. The influences of oxygen partial pressure and gas flow rate on the structures and properties of deposited films were investigated. Varying oxygen partial pressure leads to the synthesis of Cu₂O, Cu₄O₃ and CuO with different microstructures. At a constant oxygen partial pressure of 6.6 × 10^− 2 Pa, the single Cu₂O films can be obtained when the gas flow rate is below 80 sccm. The as-deposited Cu₂O thin films have a very high absorption in the visible region resulting in the visible-light induced photocatalytic activity.     

Application of pulsed laser deposited zinc oxide films to thin film transistor device

Transparent zinc oxide (ZnO) thin films were deposited on various substrates using a pulsed laser deposition (PLD) technique. During the PLD, oxygen pressure and substrate temperature were varied in order to find an optimal preparation condition of ZnO for thin film transistor (TFT) application. Dependence of optical, electrical and crystalline properties on the deposition conditions was investigated. The ZnO thin films were then deposited on SiN/c-Si layer structures in order to fabricate a TFT device. The pulsed laser deposited ZnO films showed a remarkable TFT performance: field effect mobility (μ_FE) of 2.4-12.85 cm²/V s and ratio of on and off current (R_on/off) in 2-6 order range. Influence of ZnO preparation conditions on the resulting TFT performance was discussed.     

Large nonlinear optical response of a Bi1.5Zn1.0Nb1.5O7 thin film fabricated by pulsed laser deposition

The Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin film has been fabricated on MgO (001) substrate by pulsed laser deposition. The nonlinear optical properties of the BZN film were investigated using Z-scan technique at a wavelength of 532 nm with 25 ps pulse duration. The two-photon absorption coefficient and the nonlinear refractive index of the BZN film were obtained to be 4.2 × 10^− 6 cm/W and 1.6 × 10^− 10 cm²/W respectively, which are comparable with those of some representative nonlinear optical materials. The large and fast response optical nonlinearities indicated that the BZN film is a promising candidate for future photonics devices.     

Effect of Ag doping on the performance of ZnO thin film transistor

Ag-doped zinc oxide (SZO) thin film transistors (TFTs) have been fabricated using a back-gate structure on thermally oxidized and heavily doped p-Si (100) substrate. The SZO thin films were deposited via pulsed laser deposition (PLD) from a 1, 3, and 5 wt.% Ag-doped ZnO (1SZO, 3SZO, and 5SZO, respectively) target using a KrF excimer laser (λ, 248 nm) at oxygen pressure of 350 mTorr. The deposition carried out at both room-temperature (RT) and 200 °C. The SZO thin films had polycrystalline phase with preferred growth direction of (002) as well as a wurtzite hexagonal structure. Compare with ZnO thin films, the SZO thin films were characterized by confirming the shift of (002) peak to investigate the substitution of Ag dopants for Zn sites. The as-grown SZO TFTs deposited at RT and 200 °C showed insulator characteristics. However the SZO TFTs annealed at 500 °C showed good n-type TFT performance because Ag was diffused from Zn lattice site and bound themselves at the high temperature, and it caused generation of electron carriers. The post-annealed 5SZO TFT deposited at 500 °C exhibited a threshold voltage (V_th) of 11.5 V, a subthreshold swing (SS) of 2.59 V/decade, an acceptable mobility (μ_SAT) of 0.874 cm²/V s, and on-to-off current ratios (I_on/off) of 1.44 × 10⁸.     

Zinc cadmium oxide thin film transistors fabricated at room temperature

Zinc cadmium oxide (ZnCdO) transparent thin film transistors (TFTs) have been fabricated with a back-gate structure using highly p-type Si (001) substrate. For the active channel, 30 nm, 50 nm, and 100 nm thick ZnCdO thin films were grown by pulsed laser deposition. The ZnCdO thin films were wurtzite hexagonal structure with preferred growth along the (002) direction. All the samples were found to be highly transparent with an average transmission of about 80%~ in the visible range. We have investigated the change of the performance of ZnCdO TFTs as the thickness of the active layer is increased. The carrier concentration of ZnCdO thin films has been confirmed to be increased from 10¹⁶ to 10¹⁹ cm⁻³ as the film thickness increased from 30 to 100 nm. Base on this result, the ZnCdO TFTs show a thickness-dependent performance which is ascribed to the carrier concentration in the active layer. The ZnCdO TFT with 30 nm active layer showed good off-current characteristic of below ~ 10¹¹, threshold voltage of 4.69 V, a subthreshold swing of 4.2 V/decade, mobility of 0.17 cm²/V s, and on-to-off current ratios of 3.37 × 10⁴.     

A simplified chemical synthesis of Cu2O films with periodic pattern transfer

A simple approach is discovered for the synthesis of Cu₂O films with periodic dimension transfer from sphere, rod to cone by chemical bath deposition technique. This two-step process consists of first immersing substrates into a copper thiosulfate solution followed by a subsequent dip in NaOH. The size and morphology of Cu₂O films can be controlled by tuning the concentration of NaOH solution and adjusting immersion cycles (deposition times). Three-dimensional sphere, one-dimensional rod and three-dimensional cone Cu₂O films can be periodically formed with the increase of the immersion cycles when the concentration of NaOH solution is less than 1.2 M and the immersion cycles are more than 10. The growth mechanism for such periodic pattern transfer of Cu₂O films has been investigated and proposed. The photovoltaic characteristics of Cu₂O films demonstrate that rod-like and cone-like Cu₂O films have better photoelectric property than sphere-like Cu₂O film under visible-light irradiation. This facile method may be used for the synthesis of other metal oxides films with special structures and good properties.     

Influence of Cu2O surface treatment on the photovoltaic properties of Al-doped ZnO/Cu2O solar cells

Low cost Al-doped ZnO (AZO)/Cu₂O Schottky barrier solar cells with a high conversion efficiency of 2.19% were fabricated by depositing a transparent conducting AZO thin film on high quality Cu₂O sheets prepared by thermally oxidizing copper sheets. To achieve efficiencies higher than 2%, it is necessary to form the AZO thin film at a low deposition temperature using a low-damage deposition method, i.e., at room temperature by a pulsed laser deposition. In addition, the obtained efficiency could be enhanced with a surface treatment of the Cu₂O sheets, such as by applying a Pd-Sn catalyst layer as a coating or a rapid thermal annealing treatment at approximately 500 °C in air.     

When Pt meets BaTiO3: Interaction between metal nanoparticles and oxide thin films

With the help of a focused ion beam, we can control the location of BaTiO₃ (BTO) grains during pulsed laser deposition by the use of metal nanoparticles seeds as templates. The metal nanoparticles act as nucleation sites on which to grow the BTO grains. Combined with recent work where control of BTO grain orientation was successfully demonstrated [Thin Solid Films, 518, 5806 (2010)], we can widely use the method to deposit various oxide nanoparticles in particular locations with controlled size and orientation. Such an approach could be useful for nanotechnology and device fabrication.     

Crystallization and electrical resistivity of Cu2O and CuO obtained by thermal oxidation of Cu thin films on SiO2/Si substrates

In this work, we study the crystallization and electrical resistivity of the formed oxides in a Cu/SiO₂/Si thin film after thermal oxidation by ex-situ annealing at different temperatures up to 1000 °C. Upon increasing the annealing temperature, from the X ray diffractogram the phase evolution Cu → Cu + Cu₂O → Cu₂O → Cu₂O + CuO → CuO was detected. Pure Cu₂O films are obtained at 200 °C, whereas uniform CuO films without structural surface defects such as terraces, kinks, porosity or cracks are obtained in the temperature range 300-550 °C. In both oxides, crystallization improves with annealing temperature. A resistivity phase diagram, which is obtained from the current-voltage response, is presented here. The resistivity was expected to increase linearly as a function of the annealing temperature due to evolution of oxides. However, anomalous decreases are observed at different temperatures ranges, this may be related to the improvement of the crystallization and crystallite size when the temperature increases.     

Growth behavior and optical properties of N-doped Cu2O films

N-doped Cu₂O films are deposited by sputtering a CuO target in the mixture of Ar and N₂. The structures zand optical properties have been studied for the films deposited at different temperatures. It is found that N-doping can suppress the formation of CuO phase in the films. The films are highly (100) textured at low temperatures and gradually change to be highly (111) textured at the temperature of 500 °C. With the analysis of (111) and (100) grain sizes, the surface free energy and grain size of critical nuclei are suggested to dominate the film texture. The analysis of the atomic force microscopy shows that the film growth can be attributed to the surface-diffusion-dominated growth. The forbidden rule of band gap transition is found disabled in the N-doped Cu₂O films, which can be attributed to the occupation of 2p electrons of nitrogen at the top of valence band. The optical band gap energy is determined to be 2.52 ± 0.03 eV for the films deposited at different temperatures.     

Optical properties of the c-axis oriented LiNbO3 thin film

C-axis oriented Lithium Niobate (LiNbO₃) thin films have been deposited onto epitaxially matched (001) sapphire substrate using pulsed laser deposition technique. Structural and optical properties of the thin films have been studied using the X-ray diffraction (XRD) and UV-Visible spectroscopy respectively. Raman spectroscopy has been used to study the optical phonon modes and defects in the c-axis oriented LiNbO₃ thin films. XRD analysis indicates the presence of stress in the as-grown LiNbO₃ thin films and is attributed to the small lattice mismatch between LiNbO₃ and sapphire. Refractive index (n = 2.13 at 640 nm) of the (006) LiNbO₃ thin films was found to be slightly lower from the corresponding bulk value (n = 2.28). Various factors responsible for the deviation in the refractive index of (006) LiNbO₃ thin films from the corresponding bulk value are discussed and the deviation is mainly attributed to the lattice contraction due to the presence of stress in deposited film.     

Growth of CuInO2 thin film using highly dense Cu2O-In2O3 composite targets

It is reported that CuInO₂ single phase is hardly obtainable by using the general mixed oxide synthesis route [M. Shimode, M. Sasaki, K. Mukaida, J. Solid State Chem. 151(1) (2000) 16.; L. Liu, K. Bai, H. Gong, P. Wu, Phys. Rev. B 72(12) (2005) 1252041.; H. Hahnn, C. Lorent, Z. Anorg. Allg. Chem. 279 (1955) 281.]. Therefore, the manufacturing of highly dense single phase targets for CuInO₂ thin film growing is still challenging. In this study, a Cu₂O-In₂O₃ composite target instead of a CuInO₂ single phase target was fabricated by using the general mixed oxide synthesis route. Thin films of CuInO₂ were grown on sapphire substrates by a pulsed laser deposition (PLD) process under various conditions, and c-axis oriented single phase CuInO₂ thin films were grown successfully when oxygen partial pressure was controlled.     

Controlled growth and characteristics of single-phase Cu2O and CuO films by pulsed laser deposition

Copper oxide, Cu₂O and CuO, thin films have been synthesized on Si (100) substrates using pulsed laser deposition method. The influences of substrate temperature and oxygen pressure on the structural properties of copper oxide films were discussed. The X-ray diffraction results show that the structure of the films changes from Cu₂O to CuO phase with the increasing of the oxygen pressure. It is also found that the (200) and (111) preferred Cu₂O films can be modified by changing substrate temperature. The formation of Cu₂O and CuO films are further identified by Fourier transform infrared spectroscopy. For the Cu₂O films, X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface. In addition, the optical gaps of Cu₂O and CuO films have been determined by measuring the transmittance and reflectance spectra.     

Intrinsic defects and metastability effects in Cu2O

Cu₂O based junctions (both Schottky and ZnO/Cu₂O heterojunctions) exhibit a metastable capacitance increase after illumination or reverse bias application. We show that this effect is related to the persistent photoconductivity in Cu₂O substrates. To obtain a quantitative evaluation of defect properties we have measured conductivity vs T, Capacitance-Voltage, persistent photoconductivity decay and capacitance transient at different temperatures.We show that it is impossible to explain these data using an electronic mechanism only. A new model which includes the formation-dissociation of intrinsic defect complexes (V_Cu-V_O) can give instead a better agreement with the experimental data.     

Luminescence of Cr-doped ZnGa2O4 thin films deposited by pulsed laser ablation

Chromium-doped zinc gallate powder is synthesized via a solid-state reaction and subsequently deposited as a thin film on quartz substrates by using a pulsed laser deposition technique under two different deposition conditions. The films are characterized with X-ray diffraction, scanning electron microscopy, UV-vis spectrophotometry and luminescent measurements. As the oxygen pressure is changed from 0 to 1 Pa, we find that the grain size gets smaller, the crystallinity improves, the band-gap energy increases, the excitation peaks of the charge transfer band exhibit a remarkable blue-shift from 263 to 247 nm and the intensity of the red emission (694 nm) is enhanced. The results suggest that the structural and luminescent properties of ZnGa₂O₄:Cr^3 + thin film phosphors are improved by deposition at an oxygen pressure of 1 Pa.     

Enhanced crystal grain size by bromine doping in electrodeposited Cu2O

Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu₂O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 μm² in area, or ~ 100 μm in linear dimension, while the film is only 1-5 μm thick. The enhanced grain size is explained by the effect of over-potential for the Cu²⁺/Cu⁺ redox couple on nucleation density of Cu₂O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu₂O displays a high resistivity of 100 MΩcm. Bromine doping in Cu₂O significantly reduces the resistivity to as low as 42 Ωcm after vacuum annealing. Br-doped Cu₂O shows n-type behavior.     

Synthesis of Cu2O bi-pyramids by reduction of Cu(OH)2 in solution

In this paper we describe the synthesis of Cu₂O bi-pyramids by reduction of Cu(OH)₂ using hydrazine as reducing agent. Copper chloride is used as a precursor to produce copper hydroxide in aqueous solution and the precipitation of the product is controlled by a slow addition of the reducing agent. All the reactions have been carried out at room temperature and atmospheric pressure with high repeatability. The purification process does not require expensive methods since a solid product is obtained from a reaction in liquid phase. Scanning and Transmission electron microscopy characterization showed interesting bi-pyramidal structures of several microns of edge and different sizes.